1. Technical Field
The present invention is related to a thermoplastic vulcanizate; more particularly to a thermoplastic vulcanizate composition, a method of forming the thermoplastic vulcanizate including the composition and a product thereof.
2. Description of Related Art
General requirements for soles of sports shoes, usually include good performance in elasticity, hardness, abrasion resistance, impact resistance and grip. Common materials for the sports shoes include rubber, polyurethane (PU) and ethylene/vinyl acetate copolymer (EVA), etc. Among them, the rubber is the most popular material for forming the outsole of the shoes since the rubber has excellent grip, elasticity, and elongation. However, the rubber outsole includes some drawbacks, such as heavy weight and high manufacturing cost. Moreover, the rubber outsole has a poor ozone resistance. The ozone molecules included in the environment easily react with the carbon-carbon double bonds of the rubber material and result in breaking of the carbon chains of the rubber. Hence, the elasticity of the rubber is weakened and cracking of the rubber products occurs. However, there is usually small amounts of ozone in the air, especially in the rainy days, or around a laser printer. The ozone molecules always gradually degrade the rubber products.
A material having elasticity similar to rubber, thermoplastic polyurethane (TPU), is a plastic material that has been gradually taken seriously because of its excellent mechanical strength, good elasticity, abrasion resistance and aging resistance, and has been adopted to replace PVC (polyvinyl chloride) in many products. TPU is a multi-block copolymer consisting of alternating sequences of hard and soft segments. TPU can be formed from diisocyanate (including Diphenylmethane Diisocyanate (MDI) and Toluene Diisocyanate (TDI)), high molecular weight polyols (including polyester, polyol and polycarbonate) which constitute soft segments in the PU chains, and small molecular weight polyols (including aliphatic diols and aromatic diols) which constitute hard segments in the PU chains. Since TPU both contains soft segments and hard segments, a hardness thereof can be adjusted by changing its composition. Hence, TPU can have a wide range of hardness. TPU has excellent tensile resistance, elongation, abrasion resistance and tear resistance. Moreover, TPU has good aging resistance. In addition, TPU is a thermoplastic material and has good processing characteristic. TPU can be applied to multiple kinds of processing methods, such as extrusion, calendaring, kneading and injection-molding, for manufacturing products. All of TPU products are recyclable and meet the requirement for environmental protection. However, TPU has a poor grip and is not suitable for forming shoe outsoles.
To improve the grip of TPU, a melt-blending process of rubber and thermoplastic polymers was used in the conventional arts. For example, TPU and ethylene-propylene-diene monomer (EPDM) are mixed together to increase the tensile strength of TPU. Besides, by adding EPDM into TPU, the temperature influence on TPU processing can be minimized Dynamic vulcanization is another method for improving the physical properties of TPU. Dynamic vulcanization includes vulcanizing rubber during the melt-blending process of thermoplastic polymers and rubbers. During the dynamic vulcanization process, the crosslinked rubbers can be uniformly dispersed in the continuous phase of thermoplastic polymers, such as TPU. Thermoplastic vulcanizate (TPV) can be obtained after the dynamic vulcanization process of TPU and rubber. Since TPV is composed of rubber and thermoplastic polymers, TPV can have both of the good performance and characteristic of rubber and thermoplastic polymers.
Referring to WO 2001010950A1, a method of forming TPV by dynamic vulcanization of TPU and Isoprene rubber/Ethylene Propylene Rubber (EPDM) had been disclosed. In the disclosure of WO 2001010950A1, different additives are utilized to improve the characteristic of TPV. However, it does not disclose an optimum composition of TPU and rubber for forming TPV.